Scalable Video Coding and Transport Over Broad-band wireless networks Authors: D. Wu, Y. Hou, and Y.-Q. Zhang Source: Proceedings of the IEEE, Volume: 89, Issue: 1, Jan 2001, pp Presented by: Yu Hen Hu Presentation of Research Paper

© by Yu Hen Hu2 Overview Issues of wireless transmission of video Scalable video coding Network-aware end system Adaptive Service

© by Yu Hen Hu3 Wireless Video Communication System Source Coding Packetize, FEC Pre- processing Source Decoding Post- processing Time varying wireless channel Network queue Wireless transmitter error resilience Network layer Physical layer Packet recovery Network protocol Wireless receiver Network layer Physical layer error concealment

© by Yu Hen Hu4 Application: Video Communication Encoded video –Consists of many segments of bit streams. –Bits highly dependent within each segment –Rate vary dramatically with type of frames, motion, etc. –Not all bits need to be transmitted – lossy compression –Deadline exists for each segment. QoS –Subjective perceptual visual quality –Objective visual quality measures: PSNR, etc. Control parameters –SNR scalability: Quantization levels –Spatial, temporal scalability: Frame rate, frame size –Data partitioning –Entropy coding method –Type of frames, macro- blocks, etc.

© by Yu Hen Hu5 Characteristics of Wireless Video Links High BER (bit error rate) –Due to fading channels (multi-path, shadowing) Bandwidth variations –Movement of mobile unit –Hand-off between basestations –Noisy channel causes retransmission Heterogeneity of end terminals –For multi-cast, and broadcast wireless system, one video stream serves multiple destinations with terminals of different capabilities.

© by Yu Hen Hu6 Physical: Wireless Channels Time varying channel characteristics (physical layer) –Fading –Interferences –Mobile clients –Noise –Channel estimation required. Shared spectrum –Limited bandwidth –Sharing in both local spatial and local temporal domains Resource constrained –Low power –Small form factor display QoS measures –BER (bit error rate) Control parameters –Transmission power –Modulation methods (soft- radio) Impacts on network packet delivery –Delay –Transmission Error –Mis-match between bandwidth demand and available effective BW.

© by Yu Hen Hu7 Uni-cast VS Multi-Cast Uni-cast One stream serves one receiver Can not scale up Multi-cast One stream serves multiple receivers Packets need to be duplicated and transcoded scalable

© by Yu Hen Hu8 Adaptive Service Framework

© by Yu Hen Hu9 Scalable Video Coding Partition of video into layers SNR scalability: Different quantization levels Spatial scalability: Different resolutions Temporal scalability: Different frame rate

© by Yu Hen Hu10 SNR Scalability SNR Scalable Encoder Quantizer Q at enhancement layer has smaller quantization steps Example: DCT coefficient: Base layer quantized output: 0.12 Enhancement layer input: Enhancement layer output:

© by Yu Hen Hu11 Spatial and Temporal Scalability Lower layer bit streams are obtained from down- sampled raw video. x = y n + upsample (y n-1 + upsample (y n-2 + upsample (y n-3 + … + upsample(y 0 ) …)) Down-sampling and up- sampling are performed in both spatial and temporal domain. Spatial domain: frame size Temporal domain: frame rate

© by Yu Hen Hu12 Applications of Scalable Video Coding to Wireless Channels Adapt to multiple terminal characteristics –Each terminal (receiver) subscribes to different amount of video layers according to its own capability. Adapt to variable band-width –Send appropriate amount of video layers for the currently available band-width Network supports are needed to achieve above goals

© by Yu Hen Hu13 Network aware rate scaling If network condition (available rate) is known, –encoder can optimize the encoding decision to maximize the perceptual quality subject to rate constraint. –Rate control buffer size may be adjusted to avoid buffer overrun Encoding decisions that affect rate include: –Quantization level –Coding mode (Intra, inter) selection. –Frame rate –Sending or dropping enhancement layer

© by Yu Hen Hu14 Network Monitoring CriteriaType of monitoring MethodPassiveActive FrequencyOn-demandContinuous ReplicationCentralizeddistributed

© by Yu Hen Hu15 Architecture of scalable video transportation from mobile to wired terminal Network monitoring and adaptation

© by Yu Hen Hu16 Adaptive Services Goal: –Rearrange network resources to meet the demand of wireless video transport Strategy –Reserve minimum bandwidth for base- layer video stream –Adapt resources for enhance layer stream via traffic shaping Method –Service contract: specify traffic characteristics and QoS requirement –Call admission control and resource reservation Ensure enough resources are available for individual services –Mobile multicast Guarantee QoS during handoff –Sub-stream shaping

© by Yu Hen Hu17 Transporting from Wired to Mobile Terminals

© by Yu Hen Hu18 Sub-stream Traffic Shaping

© by Yu Hen Hu19 Link Layer Error Control: ARQ and RCPC ARQ (automatic repeat request) is a link layer error control method. Resend only upon request from receiving end. Advantage: –efficient usage of BW Disadvantage: –Delay unbound RCPC: rate- compatible punctured convolution: –If too late, don’t send

© by Yu Hen Hu20 Service Comparison ServicesGuaranteedAdaptive-base Adaptive – enhanced Best-effort Path setupYYYN Traffic characteristics YYNN End-to-end QoS guarantee YIf neededNN Network feedbackNNIf neededN Resource reservation YYNN QoS Bounded delay, zero loss Small delay, low loss Better than best effort N Target Applications Non-adaptive CBR/VBR Adaptive CBR/VBR None-real time